In the semiconductor fabrication and processing industries, the ability to quickly and rapidly remove, inspect, and sort dice of semiconductor wafers is of critical importance. Typically, after a wafer has been completed and tested, it is placed onto an adhesive film backing and sawn into individual dice. The individual dice are removed from the mounted wafer and are placed into reels of pocketed tape. Such reels are then shipped for subsequent sales, whereupon the dice are removed from the tape and installed into electronic devices. As will be readily appreciated, the more rapidly and efficiently that dice are sorted, the greater the volume of dice that are shipped from a facility. This, in turn, results in higher profit margins.
Die sorters of various designs exist in the prior art. One example can be found in U.S. Pat. No. 6,222,145 to Cook, et al. (the “Cook, et al. '145 patent”), which discloses a method for sorting integrated circuit chips. A single arm removes (“pick”) a chip from a wafer, whereupon the arm is rotated to position the chip above a detector so that the backside of the chip can be inspected. After inspection, the chip is sorted based upon one or more defects detected in the chip, such that the chip is placed into one of a plurality of trays on a moveable surface. The arm includes a vacuum pencil for facilitating removal of a die from a wafer and subsequent inspection and transfer to a tray. Another example of a prior art die sorter can be found in U.S. Pat. No. 5,654,204 to Anderson (the “Anderson '204 patent”), which discloses a die sorter that includes die alignment and probing systems adapted for the removal and inspection of individual dies from wafers.
Existing die sorters suffer from a number of disadvantages. First and foremost, existing die sorters do not operate with sufficient speed, such that dies can be rapidly removed from wafers, inspected, and sorted into reels of pocketed tape. Rather, in traditional pick and place systems, the drive axes (i.e., X-, Y-, Z-, and rotational drive axes) are usually “stacked,” such that: (i) the rotational drive motor is carried by a vertical Z-axis drive motor; (ii) the rotational and Z-axis drive motors are carried by a horizontal Y-axis drive motor; and (iii) the rotational, Z-, and Y-axis drive motors are carried by a horizontal X-axis drive motor. Such an arrangement significantly reduces the speed with which the system can operate, primarily because most of the drive motors are required to carry the load of multiple drive axes.
Additionally, existing die sorters do not provide adequate and robust inspection systems, such that the connection side of a die can be inspected after being picked from a wafer and prior to placement in a pocketed tape, and the die can be inspected after placement into the pocketed tape. Rather, in many existing systems, inspection of the connection side of a die is normally performed on a wafer prior to picking. Such an arrangement cannot adequately detect damage to connection points (bumps) of the die or edge chipping that may result from the pick process. Further, while some systems do allow for inspection of a die after a pick process (see, e.g., the Cook, et al. '145 patent), no ability is provided to inspect the die after placement into a pocketed tape. Moreover, existing die sorting systems do not provide an optical inspection system which includes multiple cameras that allow for the aforementioned die inspections, in addition to inspection of pick and place heads so that the heads are precisely calibrated during operation. Accordingly, there is a need to provide a robotic die sorter that address the foregoing limitations.